A typical capacitor, line or load switch (e.g., high-power circuit interrupters and breakers) for transmission and distribution voltages utilize contactors located inside dielectric containers, which may be located inside the high-voltage insulators. There are three contactors, one for each high voltage phase. The dielectric containers are referred to as “dead tank” when they are grounded and “live tank” when they are ungrounded and physically located within the high-voltage electric field of the power line. In this physical location, the “live tank” dielectric container electrically floats within the high voltage electric field as part of (inside) the insulator between the high voltage line terminals. The “live tank” dielectric container has the advantage of a utilizing the preexisting space within the insulators to house at least a portion of the switching equipment (at least the contactor) but provides only a small footprint in which to locate the equipment.
The “dead tank” dielectric container is grounded and therefore must be insulated from the high voltage power lines. While the “dead tank” configuration provides greater size flexibility, it requires the associated expense of providing a separate tank grounded from the high voltage power lines.
In both configurations, the contactors are physically driven by actuators (drive systems) that drive the contactors to open and close the switch. The drive system typically includes a sophisticated spring loaded toggle system and mechanical latches triggered by hand or an electronic control system. Current transformers are used to detect over-current situations indicating a need to open the switch, and controllers contain the intelligence to operate the actuators, communicate with local and remote facilities, and perform other functions.
In a conventional “live tank” arrangement, some (at least the contactors) or all of the switching equipment is located within the dielectric containers formed inside the hollow insulators. This configuration typically utilizes external CTs located at high voltage around the power lines with the contactor and the mechanically sophisticated actuator crammed into the small space provided by the dielectric container located inside the insulator. This present difficult design challenges, particularly as the voltages and associated sizes of the components increase. The line-mounted CTs are also expensive and, being located high up on the power lines, present installation and maintenance challenges for line workers.
In the “dead tank” switch configuration, on the other hand, a separate grounded tank is provided to house all or a portion of the switching equipment. In particular, all three phases of CTs and contactors along with the drive system may be located in the “dead tank” resulting in relatively large dielectric container. There is, therefore, a continuing need for an improved current transformer design for a high voltage electric power switch located inside a high voltage insulator.